With advances in technology laptop computers and hand held computing devices such as PDA's (Personal Digital Assistants) have become very popular and even pervasive. It is desirable to enable these devices to communicate in a wireless fashion such as using Infrared data communication which is becoming more common. One of the concerns in using wireless communication in portable computing devices is the useful communication range of the devices and the amount of power consumed by them, as portable devices up until now use batteries, which limit the useful power on time of the devices. The more power consumed in communication the less time the devices can be used. In addition as battery power is consumed there is typically a drop off in voltage which may affect the performance of communication devices being used. In the case of LED Infrared devices a drop off in voltage will result in a lowering of the Infrared emission with attendant range reduction or reliability in certain situations.
In addition, as portable devices may be used at varying distances from the devices with which they are communicating, it may be useful to reduce the amount of power used for communication, such as by reducing the driving voltage or current of the LED's when communication is done at closer range. This can provide longer battery life while still permitting efficient communication as lower driving current can be used for communications at close quarters, with the higher driving current being reserved for communication over longer distances.
Canadian Patent Application 2,193,782 filed Dec. 23, 1996 and assigned to IBM Canada Ltd. discloses a programmable IR communication system including the storage of commands for configuring LED drive current, however the circuitry disclosed does not appear to be capable of supplying controlled programmable current regulation over a wide voltage supply variation.
U.S. Pat. No. 5,317,307 appears to disclose a method for modulation of LED's based on power demand load leveling wherein the LED's are divided into four groups which are switch-operated to control intensity. It is not capable of operating with a single LED and does not appear to supply a regulated current.
U.S. Pat. Nos. 5,428,369 and 5,574,480 appear to relate to a pointing device using an LED having intensity which is controllable in steps; however there is no disclosure of methods or circuitry for achieving the intensity control.